Telecommunications retailers (in particular for voice) offer their individual clients or parties various call access modes (in particular for telephone calls) that are generally of the following three types:
a first access mode consists, for the individual client or party, in leasing a direct and permanent link to the communications retailer who bills the client (individual party) in particular by monitoring the (quantity of) information traffic passing over the leased link; this mode of access gives a high level of security in identifying the calling party; PA1 another access mode consists in making a voice server connected to a conventional switched telephone network available to parties; the voice server enables a party calling the communications retailer to identify his or herself by means of a client or billing account number, possibly authenticated by a code number, and to dial the number of the final destination by using the (voice frequency) keys on the telephone set, some equipment enables these operations to be automated and enables the caller to dial the desired destination directly, thereby preserving calling habits; and PA1 a third access mode is by automatic callback and requires the client (or calling party) to call the automatic callback company connected to a switched telephone network (PSTN or ISDN); with this access mode, the calling party hangs up after calling the retailer and waits for the retailer (i.e. the automatic callback company) to call back. PA1 U.S. Pat. No. 5,425,085 describes a telecommunications rerouting (diversion) device; the device described is specifically designed to be interposed between an analog telephone terminal and an STN (switched telephone network) type analog network; PA1 international application WO 88/07797 describes a unit interposed between a telephone terminal and the network; the unit is connected to a computer; and PA1 international application WO 94/28683 describes circuits for generating price signals and circuits for selecting a telecommunications service provider, as a function of the price signal. PA1 U.S. Pat. No. 5,272,748 describes a system for putting a payphone into communication with a voice information server, or with the switchboard of a taxi firm (private numbering plan); and PA1 European patent application EP 493 896 describes a system for selecting the call number of a store close to the home of the calling party in order to set up a call on the basis of a short number common a plurality of stores (single number services, such as 0 800&lt;&lt;N.degree. Vert&gt;&gt; in France). PA1 prior to transmitting the number "Z" of the destination called party, the length L of the number "Z" is calculated and information representing said length L is transmitted prior to transmitting said number "Z"; and PA1 the call is established between the calling first party and the destination third party via the intermediate party only after it has been checked that the number of the destination called party is available. PA1 for a telephone terminal: an interface module with a telephone handset and, for example, a loudspeaker; PA1 an interface module with an ISDN; PA1 a keypad or input unit, preferably together with a display or display unit; PA1 a user interface module which is connected to said input and display units; and PA1 a main terminal processing or control module which is connected to said user interface module, to said ISDN interface module, and to said handset interface module via links and controlling the operation of the terminal;
These various access modes have drawbacks. To be economic, the cost of a direct leased line requires a large quantity of telecommunications and thus a sufficiently large amount of traffic to enable individual clients to benefit from prices that are lower than those offered by locally-available service providers. Access to a retailer fitted with a voice server requires telephone users to change their habits since the dialing that must be performed by the calling party is different from direct dialing using the public numbering plan that is normally used when passing via the network service provider. In addition, this mode of access does not provide sufficient security for the call retailer concerning identification of the calling party, given that the account number and/or the code number of the calling client can be stolen and used by an unauthorized third party. In its automatic version, the voice server is handicapped to the detriment of the calling party, or of the intermediate site if access is via a free number (0 800&lt;&lt;N.degree. Vert&gt;&gt; in France) or of both of them if access is via a shared charging number (0 801&lt;&lt;N.degree. Azur&gt;&gt; or 0 802&lt;&lt;N.degree. Indigo&gt;&gt; in France), by a charge being made for calls that are ineffective or that do not terminate (busy, no answer, saturation, etc. . . . ), since an ordinary call is indeed set up prior to the desired call for the purpose of passing on call parameters concerning the desired destination party (signalling in the audio band). In certain cases that have recently been analyzed, ineffective calls can represent 10% to 15% of the telecommunications budget of the calling party using the communications retailer at the intermediate site. In the access mode that makes use of automatic callback by a retailer connected to a switched telephone network or to an integrated services digital network, the callback procedure suffers from the major drawback associated with the fact that the caller must wait for the return call made by the intermediary or by the retailer (meanwhile the caller may be called by a third party, or all accesses to a PABX may become busy).
Integrated service digital networks (ISDNs) have characteristics specified by numerous ISO, CCITT/ITU-T standards; such networks are organized as a plurality of B and D type transmission channels together with corresponding protocols; B channels (circuit mode) are dedicated mainly to carrying messages or data to be communicated; D channels (packet mode) are dedicated mainly to carrying signalling information required for controlling the B channels and for the provision of supplementary services; standards also define various types of interface, including so-called "T" and "E" interfaces, defining reference points for network architecture purposes and enabling the various items of equipment that make up the network to be interconnected.
Automatic devices are also known for selecting a telecommunications service provider for the purpose of minimizing cost and/or optimizing telecommunications quality:
Telecommunications systems are also known whereby an abridged or generic number for a service (private numbering plan) is replaced by a public number plan number taken from a memory or database:
None of those documents describes or suggests making use of ISDN functions for rerouting a call and for setting up a call very quickly, cheaply, and reliably.